Title: Biobehavioral Mechanisms Linking Personality to Health in Midlife Abstract Text: The objective of this research program is to identify biobehavioral pathways by which certain dimensions of personality confer risk or afford protection against midlife changes in biological and functional capacities germane to aging. The study comprises a ~16 year follow-up of 650 men and women who were recruited in 2001-2005 to the Adult Health and Behavior (AHAB) project, an institutional resource for the study of individual differences. Participants were 30-54 years of age at AHAB enrollment, and the baseline protocol (time-1; T1) included extensive evaluation of personality and temperament; psychiatric history and symptomatology; socio-demographics; social relationships; cognition; chronic disease risk factors and health practices; medical and medication histories; and instrumented measurement of cardiovascular, autonomic, metabolic, endocrine, immune and central nervous system functioning, as well as genetic variation in pathways related to measured phenotypes. The present project represents the second wave of AHAB data collection (T2) in an anticipated multi-wave longitudinal study of midlife aging. Here, we focus in particular on 4 personality traits relating to the experience and regulation of emotions (Neuroticism, Extraversion), interpersonal relationships (Agreeableness, Extraversion), and goal-directed behaviors (Conscientiousness), each measured by combination of peer- and self-ratings. Our primary aim is to determine whether multi-informant T1 measurements of these 4 traits and of the common variance of Neuroticism, Agreeableness and Conscientiousness represented by the latent meta-trait of Stability, as well as personality change over time, predict program outcomes at follow-up (T2) in 4 broad domains: progression of cardiometabolic risk; cognition; physical functioning; and aspects of cellular aging. Mechanistic models posit a common set of health-related behaviors and biomediators (e.g., autonomic control, inflammation), as well as trait-specific pathways via stress, affective responses, and trait-relevant behaviors. Multiple end-of-day reports are also collected on all participants to test whether trait-relevant affective and behavioral responses to naturally occurring events and social interactions in daily life mirror hypothesized pathways linking these traits to health outcomes in epidemiologic models. PROJECT TERMS: Aging; Midlife; Longitudinal Study; Personality; Behavior; Cognition; Cardiometabolic Risk; Physical Functioning; Autonomic Nervous System; Inflammation